I can see this if we recognize that what is being learned here is basically skills for getting along with and maybe occasionally pursuing goals with groups of people who already share a common interest. That's a really important skill-set for life, but it's at least a couple steps removed from the kind of civic engagement that can redress systemic injustices or strengthen community life outside of these very niche spaces.

the opportuni-ties for learning about civic engagement are no longer tethered to traditional spaces like classrooms

I'm not sure I accept the proposition that opportunities for youth to learn about civic engagement ever WERE tethered solely to classrooms. (I'm not sure which other spaces these authors consider "traditional" here.)

Digital citizenship augments our embodied citizenship, which can be limited by circumstance and safety concerns.

I've long been fascinated by these possibilities for mothers of young children (I study breastfeeding advocacy as a social movement), who are often physically constrained by their caregiving in ways that make traditional civic participation difficult. Cyberlactivism, for example, has had a huge impact on offline environments for breastfeeding families.